Fast cell reselection

ABSTRACT

A user equipment (UE) expedites cell reselection. In one instance, the UE starts a reselection timer for reselecting to a neighbor cell when a signal quality of a serving cell is determined to fall below a first threshold. The UE then expedites reselecting to the neighbor cell based on a difference between the signal quality of the serving cell and the signal quality of the neighbor cell when the signal quality of the serving cell falls below a second threshold.

BACKGROUND Field

Aspects of the present disclosure relate generally to wirelesscommunication systems, and more particularly, to expedited cellreselection.

Background

Wireless communication networks are widely deployed to provide variouscommunication services, such as telephony, video, data, messaging,broadcasts, and so on. Such networks, which are usually multiple accessnetworks, support communications for multiple users by sharing theavailable network resources. One example of such a network is theuniversal terrestrial radio access network (UTRAN). The UTRAN is theradio access network (RAN) defined as a part of the universal mobiletelecommunications system (UMTS), a third generation (3G) mobile phonetechnology supported by the 3rd Generation Partnership Project (3GPP).The UMTS, which is the successor to global system for mobilecommunications (GSM) technologies, currently supports various airinterface standards, such as wideband-code division multiple access(W-CDMA), time division-code division multiple access (TD-CDMA), andtime division-synchronous code division multiple access (TD-SCDMA). Forexample, China is pursuing TD-SCDMA as the underlying air interface inthe UTRAN architecture with its existing GSM infrastructure as the corenetwork. The UMTS also supports enhanced 3G data communicationsprotocols, such as high speed packet access (HSPA), which provideshigher data transfer speeds and capacity to associated UMTS networks.HSPA is a collection of two mobile telephony protocols, high speeddownlink packet access (HSDPA) and high speed uplink packet access(HSUPA) that extends and improves the performance of existing widebandprotocols.

As the demand for mobile broadband access continues to increase, thereexists a need for further improvements in wireless technology.Preferably, these improvements should be applicable to LTE and othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

According to one aspect of the present disclosure, a method of wirelesscommunication includes starting a reselection timer for reselecting to aneighbor cell when a signal quality of a serving cell is determined tofall below a first threshold. The method also includes speeding upreselecting to the neighbor cell based on a difference between thesignal quality of the serving cell and the signal quality of theneighbor cell when the signal quality of the serving cell falls below asecond threshold.

According to another aspect of the present disclosure, an apparatus forwireless communication includes means for starting a reselection timerfor reselecting to a neighbor cell when a signal quality of a servingcell is determined to fall below a first threshold. The apparatus mayalso include means for speeding up reselecting to the neighbor cellbased on a difference between the signal quality of the serving cell andthe signal quality of the neighbor cell when the signal quality of theserving cell falls below a second threshold.

Another aspect discloses an apparatus for wireless communication andincludes a memory and at least one processor (e.g., one or moreprocessors) coupled to the memory. The processor(s) is configured tostart a reselection timer for reselecting to a neighbor cell when asignal quality of a serving cell is determined to fall below a firstthreshold. The processor(s) is also configured to speed up reselectingto the neighbor cell based on a difference between the signal quality ofthe serving cell and the signal quality of the neighbor cell when thesignal quality of the serving cell falls below a second threshold.

Yet another aspect discloses a non-transitory computer-readable storagemedium having non-transitory program code recorded thereon which, whenexecuted by the processor(s), causes the processor(s) to start areselection timer for reselecting to a neighbor cell when a signalquality of a serving cell is determined to fall below a first threshold.The program code also causes the processor(s) to speed up reselecting tothe neighbor cell based on a difference between the signal quality ofthe serving cell and the signal quality of the neighbor cell when thesignal quality of the serving cell falls below a second threshold.

This has outlined, rather broadly, the features and technical advantagesof the present disclosure in order that the detailed description thatfollows may be better understood. Additional features and advantages ofthe disclosure will be described below. It should be appreciated bythose skilled in the art that this disclosure may be readily utilized asa basis for modifying or designing other structures for carrying out thesame purposes of the present disclosure. It should also be realized bythose skilled in the art that such equivalent constructions do notdepart from the teachings of the disclosure as set forth in the appendedclaims. The novel features, which are believed to be characteristic ofthe disclosure, both as to its organization and method of operation,together with further objects and advantages, will be better understoodfrom the following description when considered in connection with theaccompanying figures. It is to be expressly understood, however, thateach of the figures is provided for the purpose of illustration anddescription only and is not intended as a definition of the limits ofthe present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, nature, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout.

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of a downlink framestructure in long term evolution (LTE).

FIG. 3 is a diagram illustrating an example of an uplink frame structurein long term evolution (LTE).

FIG. 4 is a block diagram conceptually illustrating an example of atelecommunications system employing a time division synchronous codedivision multiple access (TD-SCDMA) standard.

FIG. 5 is a block diagram conceptually illustrating an example of aframe structure for a time division synchronous code division multipleaccess carrier.

FIG. 6 is a block diagram conceptually illustrating an example of a basestation in communication with a user equipment (UE) in atelecommunications system.

FIG. 7 is a diagram illustrating network coverage areas according toaspects of the present disclosure.

FIG. 8 is a block diagram illustrating the measurement and evaluation ofthe serving cell and intra/inter-frequency cells.

cells according to one aspect of the present disclosure.

FIG. 9 is flow diagram illustrating an example process according toaspects of the present disclosure.

FIG. 10 is a is a block diagram illustrating the measurement andevaluation of the serving cell and intra/inter-frequency cells.according to one aspect of the present disclosure.

FIG. 11 is a block diagram illustrating a method for expediting cellreselection according to one aspect of the present disclosure.

FIG. 12 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system accordingto one aspect of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

FIG. 1 is a diagram illustrating a network architecture 100 of alongterm evolution (LTE) network. The LTE network architecture 100 maybe referred to as an evolved packet system (EPS) 100. The EPS 100 mayinclude one or more user equipment (UE) 102, an evolved UMTS terrestrialradio access network (E-UTRAN) 104, an evolved packet core (EPC) 110, ahome subscriber server (HSS) 120, and an operator's IP services 122. TheEPS can interconnect with other access networks, but for simplicitythose entities/interfaces are not shown. As shown, the EPS 100 providespacket-switched services, however, as those skilled in the art willreadily appreciate, the various concepts presented throughout thisdisclosure may be extended to networks providing circuit-switchedservices.

The E-UTRAN 104 includes an evolved Node B (eNodeB) 106 and othereNodeBs 108. The eNodeB 106 provides user and control plane protocolterminations toward the UE 102. The eNodeB 106 may be connected to theother eNodeBs 108 via a backhaul (e.g., an X2 interface). The eNodeB 106may also be referred to as a base station, a base transceiver station, aradio base station, a radio transceiver, a transceiver function, a basicservice set (BSS), an extended service set (ESS), or some other suitableterminology. The eNodeB 106 provides an access point to the EPC 110 fora UE 102. Examples of UEs 102 include a cellular phone, a smart phone, asession initiation protocol (SIP) phone, a laptop, a notebook, anetbook, a smartbook, a personal digital assistant (PDA), a satelliteradio, a global positioning system, a multimedia device, a video device,a digital audio player (e.g., MP3 player), a camera, a game console, orany other similar functioning device. The UE 102 may also be referred toby those skilled in the art as a mobile station or apparatus, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

The eNodeB 106 is connected to the EPC 110 via, e.g., an S1 interface.The EPC 110 includes a mobility management entity (MME) 112, other MMES114, a serving gateway 116, and a packet data network (PDN) gateway 118.The MME 112 is the control node that processes the signaling between theUE 102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theserving gateway 116, which itself is connected to the PDN gateway 118.The PDN gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN gateway 118 is connected to the operator's IPservices 122. The operator's IP services 122 may include the Internet,the Intranet, an IP multimedia subsystem (IMS), and a PS streamingservice (PSS).

FIG. 2 is a diagram 200 illustrating an example of a downlink framestructure in LTE. A frame (10 ms) may be divided into 10 equally sizedsubframes. Each subframe may include two consecutive time slots. Aresource grid may be used to represent two time slots, each time slotincluding a resource block. The resource grid is divided into multipleresource elements. In LTE, a resource block contains 12 consecutivesubcarriers in the frequency domain and, for a normal cyclic prefix ineach OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84resource elements. For an extended cyclic prefix, a resource blockcontains 6 consecutive OFDM symbols in the time domain and has 72resource elements. Some of the resource elements, as indicated as R 202,204, include downlink reference signals (DL-RS). The DL-RS includecell-specific RS (CRS) (also sometimes called common RS) 202 andUE-specific RS (UE-RS) 204. UE-RS 204 are transmitted only on theresource blocks upon which the corresponding physical downlink sharedchannel (PDSCH) is mapped. The number of bits carried by each resourceelement depends on the modulation scheme. Thus, the more resource blocksthat a UE receives and the higher the modulation scheme, the higher thedata rate for the UE.

FIG. 3 is a diagram 300 illustrating an example of an uplink framestructure in LTE. The available resource blocks for the uplink may bepartitioned into a data section and a control section. The controlsection may be formed at the two edges of the system bandwidth and mayhave a configurable size. The resource blocks in the control section maybe assigned to UEs for transmission of control information. The datasection may include all resource blocks not included in the controlsection. The uplink frame structure results in the data sectionincluding contiguous subcarriers, which may allow a single UE to beassigned all of the contiguous subcarriers in the data section.

A UE may be assigned resource blocks 310 a, 310 b in the control sectionto transmit control information to an eNodeB. The UE may also beassigned resource blocks 320 a, 320 b in the data section to transmitdata to the eNodeB. The UE may transmit control information in aphysical uplink control channel (PUCCH) on the assigned resource blocksin the control section. The UE may transmit only data or both data andcontrol information in a physical uplink shared channel (PUSCH) on theassigned resource blocks in the data section. An uplink transmission mayspan both slots of a subframe and may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve uplink synchronization in a physical random access channel(PRACH) 330. The PRACH 330 carries a random sequence and cannot carryany uplink data/signaling. Each random access preamble occupies abandwidth corresponding to six consecutive resource blocks. The startingfrequency is specified by the network. That is, the transmission of therandom access preamble is restricted to certain time and frequencyresources. There is no frequency hopping for the PRACH. The PRACHattempt is carried in a single subframe (1 ms) or in a sequence of fewcontiguous subframes and a UE can make only a single PRACH attempt perframe (10 ms).

Turning now to FIG. 4, a block diagram is shown illustrating an exampleof a telecommunications system 400. The various concepts presentedthroughout this disclosure may be implemented across a broad variety oftelecommunication systems, network architectures, and communicationstandards. By way of example and without limitation, the aspects of thepresent disclosure illustrated in FIG. 4 are presented with reference toa UMTS system employing a TD-SCDMA standard. In this example, the UMTSsystem includes a radio access network (RAN) 402 (e.g., UTRAN) thatprovides various wireless services including telephony, video, data,messaging, broadcasts, and/or other services. The RAN 402 may be dividedinto a number of radio network subsystems (RNSs) such as an RNS 407,each controlled by a radio network controller (RNC), such as an RNC 406.For clarity, only the RNC 406 and the RNS 407 are shown; however, theRAN 402 may include any number of RNCs and RNSs in addition to the RNC406 and RNS 407. The RNC 406 is an apparatus responsible for, amongother things, assigning, reconfiguring and releasing radio resourceswithin the RNS 407. The RNC 406 may be interconnected to other RNCs (notshown) in the RAN 402 through various types of interfaces such as adirect physical connection, a virtual network, or the like, using anysuitable transport network.

The geographic region covered by the RNS 407 may be divided into anumber of cells, with a radio transceiver apparatus serving each cell. Aradio transceiver apparatus is commonly referred to as a node B in UMTSapplications, but may also be referred to by those skilled in the art asa base station (BS), a base transceiver station (BTS), a radio basestation, a radio transceiver, a transceiver function, a basic serviceset (BSS), an extended service set (ESS), an access point (AP), or someother suitable terminology. For clarity, two node Bs 408 are shown;however, the RNS 407 may include any number of wireless node Bs. Thenode Bs 408 provide wireless access points to a core network 404 for anynumber of mobile apparatuses. For illustrative purposes, three UEs 410are shown in communication with the node Bs 408. The downlink (DL), alsocalled the forward link, refers to the communication link from a node Bto a UE, and the uplink (UL), also called the reverse link, refers tothe communication link from a UE to a node B.

The core network 404, as shown, includes a GSM core network. However, asthose skilled in the art will recognize, the various concepts presentedthroughout this disclosure may be implemented in a RAN, or othersuitable access network, to provide UEs with access to types of corenetworks other than GSM networks.

In this example, the core network 404 supports circuit-switched serviceswith a mobile switching center (MSC) 412 and a gateway MSC (GMSC) 414.One or more RNCs, such as the RNC 406, may be connected to the MSC 412.The MSC 412 is an apparatus that controls call setup, call routing, andUE mobility functions. The MSC 412 also includes a visitor locationregister (VLR) (not shown) that contains subscriber-related informationfor the duration that a UE is in the coverage area of the MSC 412. TheGMSC 414 provides a gateway through the MSC 412 for the UE to access acircuit-switched network 416. The GMSC 414 includes a home locationregister (HLR) (not shown) containing subscriber data, such as the datareflecting the details of the services to which a particular user hassubscribed. The HLR is also associated with an authentication center(AuC) that contains subscriber-specific authentication data. When a callis received for a particular UE, the GMSC 414 queries the HLR todetermine the UE's location and forwards the call to the particular MSCserving that location.

The core network 404 also supports packet-data services with a servingGPRS support node (SGSN) 418 and a gateway GPRS support node (GGSN) 420.General packet radio service (GPRS) is designed to provide packet-dataservices at speeds higher than those available with standard GSMcircuit-switched data services. The GGSN 420 provides a connection forthe RAN 402 to a packet-based network 422. The packet-based network 422may be the Internet, a private data network, or some other suitablepacket-based network. The primary function of the GGSN 420 is to providethe UEs 410 with packet-based network connectivity. Data packets aretransferred between the GGSN 420 and the UEs 410 through the SGSN 418,which performs primarily the same functions in the packet-based domainas the MSC 412 performs in the circuit-switched domain.

The UMTS air interface is a spread spectrum direct-sequence codedivision multiple access (DS-CDMA) system. The spread spectrum DS-CDMAspreads user data over a much wider bandwidth through multiplication bya sequence of pseudorandom bits called chips. The TD-SCDMA standard isbased on such direct sequence spread spectrum technology andadditionally calls for a time division duplexing (TDD), rather than afrequency division duplexing (FDD) as used in many FDD mode UMTS/W-CDMAsystems. TDD uses the same carrier frequency for both the uplink (UL)and downlink (DL) between a node B 408 and a UE 410, but divides uplinkand downlink transmissions into different time slots in the carrier.

FIG. 5 shows a frame structure 500 for a TD-SCDMA carrier. The TD-SCDMAcarrier, as illustrated, has a frame 502 that is 10 ms in length. Thechip rate in TD-SCDMA is 1.28 Mcps. The frame 502 has two 5 mssubframes504, and each of the subframes 504 includes seven time slots, TS0through TS6. The first time slot, TS0, is usually allocated for downlinkcommunication, while the second time slot, TS1, is usually allocated foruplink communication. The remaining time slots, TS2 through TS6, may beused for either uplink or downlink, which allows for greater flexibilityduring times of higher data transmission times in either the uplink ordownlink directions. A downlink pilot time slot (DwPTS) 506, a guardperiod (GP) 508, and an uplink pilot time slot (UpPTS) 510 (also knownas the uplink pilot channel (UpPCH)) are located between TS0 and TS1.Each time slot, TS0-TS6, may allow data transmission multiplexed on amaximum of 16 code channels. Data transmission on a code channelincludes two data portions 512 (each with a length of 352 chips)separated by a midamble 514 (with a length of 144 chips) and followed bya guard period (GP) 516 (with a length of 16 chips). The midamble 514may be used for features, such as channel estimation, while the guardperiod 516 may be used to avoid inter-burst interference. Alsotransmitted in the data portion is some Layer 1 control information,including synchronization shift (SS) bits 518. Synchronization shiftbits 518 only appear in the second part of the data portion. Thesynchronization shift bits 518 immediately following the midamble canindicate three cases: decrease shift, increase shift, or do nothing inthe upload transmit timing. The positions of the synchronization shiftbits 518 are not generally used during uplink communications.

FIG. 6 is a block diagram of a base station (e.g., eNodeB or node B) 610in communication with a UE 650 in an access network. In the downlink,upper layer packets from the core network are provided to acontroller/processor 675. The controller/processor 675 implements thefunctionality of the L2 layer. In the downlink, the controller/processor675 provides header compression, ciphering, packet segmentation andreordering, multiplexing between logical and transport channels, andradio resource allocations to the UE 650 based on various prioritymetrics. The controller/processor 675 is also responsible for HARQoperations, retransmission of lost packets, and signaling to the UE 650.

The TX processor 616 implements various signal processing functions forthe L1 layer (i.e., physical layer). The signal processing functionsincludes coding and interleaving to facilitate forward error correction(FEC) at the UE 650 and mapping to signal constellations based onvarious modulation schemes (e.g., binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK),M-quadrature amplitude modulation (M-QAM)). The coded and modulatedsymbols are then split into parallel streams. Each stream is then mappedto an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot)in the time and/or frequency domain, and then combined together using anInverse Fast Fourier Transform (IFFT) to produce a physical channelcarrying a time domain OFDMsymbol stream. The OFDM stream is spatiallyprecoded to produce multiple spatial streams. Channel estimates from achannel estimator 674 may be used to determine the coding and modulationscheme, as well as for spatial processing. The channel estimate may bederived from a reference signal and/or channel condition feedbacktransmitted by the UE 650. Each spatial stream is then provided to adifferent antenna 720 via a separate transmitter (TX) 618. Eachtransmitter (TX) 618 modulates an RF carrier with a respective spatialstream for transmission.

At the UE 650, each receiver (RX) 654 receives a signal through itsrespective antenna 652. Each receiver (RX) 654 recovers informationmodulated onto an RF carrier and provides the information to thereceiver (RX) processor 656. The RX processor 656 implements varioussignal processing functions of the L1 layer. The RX processor 656performs spatial processing on the information to recover any spatialstreams destined for the UE 650. If multiple spatial streams aredestined for the UE 650, they may be combined by the RX processor 656into a single OFDM symbol stream. The RX processor 656 then converts theOFDM symbol stream from the time-domain to the frequency domain using aFast Fourier Transform (FFT). The frequency domain signal comprises aseparate OFDM symbol stream for each subcarrier of the OFDM signal. Thesymbols on each subcarrier, and the reference signal, is recovered anddemodulated by determining the most likely signal constellation pointstransmitted by the base station 610. These soft decisions may be basedon channel estimates computed by the channel estimator 658. The softdecisions are then decoded and deinterleaved to recover the data andcontrol signals that were originally transmitted by the base station 610on the physical channel. The data and control signals are then providedto the controller/processor 659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the uplink, the controller/processor 659provides demultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the uplink, a data source 667 is used to provide upper layer packetsto the controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the downlink transmission by the basestation 610, the controller/processor 659 implements the L2 layer forthe user plane and the control plane by providing header compression,ciphering, packet segmentation and reordering, and multiplexing betweenlogical and transport channels based on radio resource allocations bythe base station 610. The controller/processor 659 is also responsiblefor HARQ operations, retransmission of lost packets, and signaling tothe base station 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the base station 610 may be used bythe TX processor 668 to select the appropriate coding and modulationschemes, and to facilitate spatial processing. The spatial streamsgenerated by the TX processor 668 are provided to different antenna 652via separate transmitters (TX) 654. Each transmitter (TX) 654 modulatesan RF carrier with a respective spatial stream for transmission.

The uplink transmission is processed at the base station 610 in a mannersimilar to that described in connection with the receiver function atthe UE 650. Each receiver (RX) 618 receives a signal through itsrespective antenna 620. Each receiver (RX) 618 recovers informationmodulated onto an RF carrier and provides the information to a RXprocessor 670. The RX processor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 and 659 can be associated with memories 676 and660, respectively that store program codes and data. For example, thecontroller/processors 675 and 659 may provide various functionsincluding timing, peripheral interfaces, voltage regulation, powermanagement, and other control functions. The memories 676 and 660 may bereferred to as a computer-readable media. For example, the memory 660 ofthe UE 650 may store a wireless communication module 691 which, whenexecuted by the controller/processor 659, configures the UE 650 toexpedite cell reselection according to aspects of the presentdisclosure.

In the uplink, the controller/processor 675 provides demultiplexingbetween transport and logical channels, packet reassembly, deciphering,header decompression, control signal processing to recover upper layerpackets from the UE 650. Upper layer packets from thecontroller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

Some networks may be deployed with multiple radio access technologies.FIG. 7 illustrates a network utilizing multiple types of radio accesstechnologies (RATs), such as but not limited to GSM (second generation(2G)), TD-SCDMA (third generation (3G)), LTE (fourth generation (4G))and fifth generation (5G). Multiple RATs may be deployed in a network toincrease capacity. Typically, 2G and 3G are configured with lowerpriority than 4G. Additionally, multiple frequencies within LTE (4G) mayhave equal or different priority configurations. Reselection rules aredependent upon defined RAT priorities. Different RATs are not configuredwith equal priority.

In one example, the geographical area 700 includes RAT-1 cells 702 andRAT-2 cells 704. In one example, the RAT-1 cells are 2G or 3G cells andthe RAT-2 cells are LTE cells. However, those skilled in the art willappreciate that other types of radio access technologies may be utilizedwithin the cells. A user equipment (UE) 706 may move from one cell, suchas a RAT-1 cell 702, to another cell, such as a RAT-2 cell 704. Themovement of the UE 706 may specify a handover or a cell reselection.

The handover or cell reselection may be performed when the UE moves froma coverage area of a first RAT to the coverage area of a second RAT, orvice versa. A handover or cell reselection may also be performed whenthere is a coverage hole or lack of coverage in one network, when thereis traffic balancing between a first RAT and the second RAT networks orcan be based on a type of communication desired by the UE. As part ofthat handover or cell reselection process, while in a connected mode ordiscontinuous reception mode (DRX) with a first system or RAT (e.g.,TD-SCDMA) a UE may be specified to perform activities with one or moreneighbor cells. For example, the UE may perform measurement of aneighboring cell of the first, a second and/or third RAT (such as GSMcell, LTE or TD-SCDMA). The discontinuous reception mode may includeidle mode, cell paging channel (CELL_PCH) mode, forward access channel(FACH) and universal terrestrial radio access network (UTRAN)registration area paging channel (URA_PCH) mode.

The UE may tune away from the first RAT to perform the activities at thesecond (and/or third) RAT. The activities performed when tuning away mayinclude selecting and monitoring an indicated paging indicator channel(PICH) and paging channel (PCH), monitoring for paging information ofthe second (or third) RAT, monitoring and collecting system informationof the second (or third) RAT (e.g., frequency of the second (or third)RAT), performing measurements (e.g., inter radio access technologymeasurements) for cell(s) of the first RAT and neighbor cells of thesecond (or third) RAT, executing cell reselection evaluation processes,and/or performing cell reselection to reselect to a neighbor cell of thesecond (or third) RAT when cell reselection trigger conditions are met.

In some networks, when the UE is camped on or connected to a servingcell of a first RAT, the UE may be informed of multiple neighbor cells.The neighbor cells may be of a same RAT and may have differentfrequencies or be of different RATs with same and/or differentfrequencies. For example, the UE may receive or be informed of LTEneighbor frequencies/cells with or without cell identifiers while campedon a TD-SCDMA cell. The neighbor cell information may be broadcast froma network (e.g., TD-SCDMA network). In some instances, only frequenciesof a particular RAT (e.g., LTE) are broadcasted to the UE.

In accordance with the reselection procedure, the UE performs interradio access technology (IRAT) measurement on neighbor cells (e.g., LTEneighbor cells/frequencies). For example, the UE may measure theneighbor cells of a second network for signal strength, frequencychannel, and base station identity code (BSIC). The UE may then connectto the strongest cell of the second network. Such measurement may bereferred to as inter radio access technology (IRAT) measurement.

During the IRAT measurement, if the cell reselection trigger conditionsare continuously met upon the expiration of a reselection timer (e.g.,Treselection), the serving RAT informs the target RAT to initiate cellreselection to a detected cell of the target RAT during the IRATmeasurement. The reselection timer governs when a UE may reselect to anew cell. The UE may not be permitted to reselect to a desired targetRAT until expiration of the reselection timer. Thus, the UE reselects tothe target cell if the cell reselection trigger conditions arecontinuously met upon expiration of the reselection timer. For example,a TD-SCDMA module of the UE informs an LTE module of the UE to startcell reselection to the target LTE cell/frequency detected during theIRAT measurement. The LTE module of the UE then starts acquisition onthe LTE frequency of the detected target LTE cell. The LTE module thenattempts to camp on the target LTE cell after collection of broadcastedsystem information blocks (SIBs).

As noted, after the UE determines that trigger conditions are satisfiedfor a cell reselection, the UE waits until an expiration of areselection for the UE to reselect to the new cell. In some instances,however, waiting for the expiration of the reselection of thereselection timer results in a RAT failure event. For example, the RATfailure event may include call setup failure or a dropped call when theUE attempts to perform call setup on a deteriorated serving cell.

Fast Cell Reselection

Aspects of the present disclosure are directed to expediting cellreselection from a first radio access technology (RAT) to a second RATbased on a difference between a signal quality of a cell/frequency ofthe serving RAT and a signal quality of a neighbor RAT when the signalquality of the serving cell falls below a threshold. When a userequipment (UE) is camped on the first RAT and the UE is in the coveragearea of the second RAT, the UE searches for one or more frequencies(corresponding to one or more cells) and measures signal quality of theone or more detected cells. When the results of the measurement indicatethat cell reselection trigger conditions are met, the UE starts a cellreselection timer or time to trigger. For example, the UE starts thereselection timer for reselecting to a neighbor cell when a signalquality of the neighbor cell of the second RAT is determined to exceed aneighbor cell threshold, when the signal quality of the serving cell isbelow a first threshold.

In one aspect of the disclosure, the UE speeds up reselecting to theneighbor cell based on a difference between the signal quality of theserving cell and the signal quality of the neighbor cell when the signalquality of the serving cell falls below a second threshold. For example,the UE speeds up the cell reselection when the difference between thesignal quality of the serving cell and the signal quality of theneighbor cell is above a third threshold. The cell reselection isexpedited by reselecting to the neighbor cell prior to a scheduledexpiration of the reselection timer. The reselection may occur prior toa call setup on the UE. The UE avoids dropped calls or call failure byexpediting the reselection to the neighbor cell. In one aspect of thedisclosure the each of the thresholds is independently defined by the UEand/or the network.

Cell reselection is a procedure triggered by user equipments (UEs) inidle mode to determine which cell to camp on. Cell reselection may relyon measured radio frequency (RF) quality and system parametersbroadcasted from networks. For example, a mobile UE observes (e.g.,searches and/or measures) signal quality of the serving and neighborcells.

In idle mode (as well as in (e.g., forward access channel (FACH)/cellpaging channel (CELL_PCH)/universal terrestrial radio access network(UTRAN) registration area paging channel (URA_PCH) states in connectedmode), the UE performs various activities like serving cellmeasurements, neighbor cell measurements and cell reselection.

Upon receiving a measurement request according to a radio resourcecontrol (RRC) protocol with configuration originated from a systeminformation block (SIB), a protocol layer (Layer 1) of the UE configuresthe UE for measurement and starts measuring the serving cell and othercells (intra/inter-frequency/inter-radio access technology (RAT)) asconfigured by a radio resource control (RRC).

The UE evaluates a signal quality of the serving cell to determinewhether the signal quality of the serving cell satisfies a criteria(e.g., signal strength threshold) to serve the UE. The UE also evaluatesthe signal quality of the neighbor cells to determine whether the signalquality of the neighbor cells satisfy a criteria, and ranks the neighborcells based on their measured signal quality.

If cell reselection criteria for a neighbor cell is satisfied, then theUE initiates reselection to the neighbor cell (e.g., the highest rankedneighbor cell).

Aspects of the present disclosure are directed to a fast cellreselection scheme that may be applied to networks, such as, but notlimited to, the universal mobile telecommunications system (UMTS), thetime division-code division multiple access (TD-CDMA), and long termevolution (LTE).

FIG. 8 is a diagram illustrating the measurement and evaluation of theserving cell and intra/inter-frequency cells. The measurement of theserving cell may include: measuring and evaluating serving cell Scriteria (e.g., signal quality criteria) once every discontinuousreception (DRX) cycle. If the S criteria failed for defined number(Nserv) of consecutive DRX cycles, UE initiates neighbor cellmeasurements.

For the measurement of intra/inter-frequency cells, the UE performsintra-frequency measurement if Ssery (e.g., signal quality of servingcell)<=SintraSearch (e.g., intra-frequency threshold). The UE performsinter-frequency measurements if Sserv<=SinterSearch (e.g.,inter-frequency threshold), and:

S_rxlev=Q_rxlevmeas−(Q_rxlevmin+Q_rxlevminOffset)−P_comp

The cell reselection is triggered when Treselection is expired.

FIG. 9 illustrates an example flow diagram according to an aspect of thepresent disclosure and includes the following variables:

where Qmeas,s is the signal quality/strength measurement (e.g.,reference signal received quality) of the serving cell;

Qhysts,s is an hysteresis value of the serving cell;

Qmeas,n is the signal quality/strength measurement of the neighbor cell;

Qoffset,n is an offset between the serving cell and the neighbor cell;

Srxlev (e.g., S or Sservingcell) is a cell reselection received level orvalue such as signal quality of the serving cell;

Qrxlevmin is a minimum specified or required receive level in a cell;

Qrxlevminoffset is an offset from the minimum specified or requiredreceive level in the cell;

Ppowerclass is a transmit power of the UE;

Pmax is a maximum transmit power;

Rs is a serving cell rank; and

Rn is a neighbor cell (non-serving cell) rank.

The variable S intrasearch (e.g., intra-frequency threshold) controlswhether the UE must make measurements of intra-frequency cells whilecamped on a current cell. Further, S intersearch (e.g., inter-frequencythreshold) controls whether the UE must make measurements ofinter-frequency cells while camped on a current cell. The Treselection(reselection timer) governs when the UE may reselect to a new cell.Qrxlevmeas is the current cell's reference signal received power (RSRP).Pcomp is a cower compensation value for uplink and/or downlinkcommunication.

Problems with the current approach may include call setup failure due toslow reselection. For example, call setup failure due to radio linkfailure (RLF) caused by a bad serving cell of a network (e.g., TD-SCDMA,WCDMA or LTE).

Slow reselection may cause a call drop during call setup for connectedmode. When a UE is in connected mode and wants to switch to a bettercell, handover message is easily delayed by measurement control messagesand radio bearer (RB) messages (e.g., RB3) messages, e.g., for callsetup after RRC connection setup. Downlink (DL) conditions maydeteriorate quickly resulting in call drop before the UE receives thecomplete handover message, especially for the bandwidth limited cases.

This kind of call setup failure might be avoided if the UE has a chanceto camp on a better cell before call setup, viz. to trigger a cellreselection procedure before a time to trigger (TTT) or reselectiontimer expires if the serving cell is not good enough (e.g. receivedsignal code power (RSCP) or signal quality of the serving cell is lowerthan a threshold) and there is a much better neighbor cell.

Aspects of the disclosure are applicable to WCDMA, TD-SCDMA, LTE orother radio access technologies (RATs).

FIG. 10 is a block diagram illustrating the measurement and evaluationof the serving cell and intra/inter-frequency cells. The cellreselection is triggered earlier before an expiration of a reselectiontimer, e.g., T reselection, when the following condition is satisfied:

   If (TTT is started and t<T_reselection) {  if Q_(meas,s)≤  

 Tresh 

  _fastresel and Q_(meas,n)-Q_(meas,s)≥delta (dB)    trigger cellreselection immediately; }

The Tresh_(fastresel) and delta may be configured differently fordifferent systems, where the Tresh_(fastresel) is a signalquality/strength threshold for fast reselection.

FIG. 11 shows a wireless communication method 1100 for expeditingreselection according to one aspect of the disclosure. At block 1102, auser equipment (UE) starts a reselection timer for reselecting to aneighbor cell when a signal quality of a serving cell is determined tofall below a first threshold. At block 1104, the UEspeeds up reselectingto the neighbor cell based on a difference between the signal quality ofthe serving cell and the signal quality of the neighbor cell when thesignal quality of the serving cell falls below a second threshold.

FIG. 12 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1200 employing a processing system 1214.The processing system 1214 may be implemented with a bus architecture,represented generally by the bus 1224. The bus 1224 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1214 and the overall designconstraints. The bus 1224 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1222 the modules 1202, 1204 and the non-transitory computer-readablemedium 1226. The bus 1224 may also link various other circuits such astiming sources, peripherals, voltage regulators, and power managementcircuits, which are well known in the art, and therefore, will not bedescribed any further.

The apparatus includes a processing system 1214 coupled to a transceiver1230. The transceiver 1230 is coupled to one or more antennas 1220. Thetransceiver 1230 enables communicating with various other apparatus overa transmission medium. The processing system 1214 includes a processor1222 coupled to a non-transitory computer-readable medium 1226. Theprocessor 1222 is responsible for general processing, including theexecution of software stored on the computer-readable medium 1226. Thesoftware, when executed by the processor 1222, causes the processingsystem 1214 to perform the various functions described for anyparticular apparatus. The computer-readable medium 1226 may also be usedfor storing data that is manipulated by the processor 1222 whenexecuting software.

The processing system 1214 includes a timing module 1202 for starting areselection timer for reselecting to a neighbor cell when a signalquality of a serving cell is determined to fall below a first threshold.The processing system 1214 also includes a reselecting module 1204 forspeeding up reselecting to the neighbor cell based on a differencebetween the signal quality of the serving cell and the signal quality ofthe neighbor cell when the signal quality of the serving cell fallsbelow a second threshold. The modules 1202 and 1204 may be softwaremodules running in the processor 1222, resident/stored in thecomputer-readable medium 1226, one or more hardware modules coupled tothe processor 1222, or some combination thereof. The processing system1214 may be a component of the UE 650 of FIG. 6 and may include thememory 660, and/or the controller/processor 659.

In one configuration, an apparatus such as a UE 650 is configured forwireless communication including means for starting a reselection timer.In one aspect, the reselection timer starting means may be the receiveprocessor 656, the controller/processor 659, the memory 660, thewireless communication module 691, the timing module 1202, and/or theprocessing system 1214 configured to perform the aforementioned means.In one configuration, the means functions correspond to theaforementioned structures. In another aspect, the aforementioned meansmay be a module or any apparatus configured to perform the functionsrecited by the reselection timer starting means.

The UE 650 is also configured to include means for speeding upreselecting to the neighbor cell. In one aspect, the speeding up meansmay include the antennas 652/920, the receiver 654, the transceiver1230, the receive processor 656, the controller/processor 659, thememory 660, the reselecting module 1204, and/or the processing system1214 configured to perform the functions recited by the identifyingmeans. In one configuration, the means and functions correspond to theaforementioned structures. In another aspect, the aforementioned meansmay be a module or any apparatus configured to perform the functionsrecited by the speeding up means.

Several aspects of a telecommunications system has been presented withreference to LTE, TD-SCDMA and GSM systems. As those skilled in the artwill readily appreciate, various aspects described throughout thisdisclosure may be extended to other telecommunication systems, networkarchitectures and communication standards, including those with highthroughput and low latency such as 4G systems, 5G systems and beyond. Byway of example, various aspects may be extended to other UMTS systemssuch as W-CDMA, high speed downlink packet access (HSDPA), high speeduplink packet access (HSUPA), high speed packet access plus (HSPA+) andTD-CDMA. Various aspects may also be extended to systems employing longterm evolution (LTE) (in FDD, TDD, or both modes), LTE-Advanced (LTE-A)(in FDD, TDD, or both modes), CDMA2000, evolution-data optimized(EV-DO), ultra mobile broadband (UMB), IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, Ultra-Wideband (UWB), Bluetooth, and/or othersuitable systems. The actual telecommunication standard, networkarchitecture, and/or communication standard employed will depend on thespecific application and the overall design constraints imposed on thesystem.

Several processors have been described in connection with variousapparatuses and methods. These processors may be implemented usingelectronic hardware, computer software, or any combination thereof.Whether such processors are implemented as hardware or software willdepend upon the particular application and overall design constraintsimposed on the system. By way of example, a processor, any portion of aprocessor, or any combination of processors presented in this disclosuremay be implemented with a microprocessor, microcontroller, digitalsignal processor (DSP), a field-programmable gate array (FPGA), aprogrammable logic device (PLD), a state machine, gated logic, discretehardware circuits, and other suitable processing components configuredto perform the various functions described throughout this disclosure.The functionality of a processor, any portion of a processor, or anycombination of processors presented in this disclosure may beimplemented with software being executed by a microprocessor,microcontroller, DSP, or other suitable platform.

Software shall be construed broadly to mean instructions, instructionsets, code, code segments, program code, programs, subprograms, softwaremodules, applications, software applications, software packages,routines, subroutines, objects, executables, threads of execution,procedures, functions, etc., whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise. Thesoftware may reside on a non-transitory computer-readable medium. Acomputer-readable medium may include, by way of example, memory such asa magnetic storage device (e.g., hard disk, floppy disk, magneticstrip), an optical disk (e.g., compact disc (CD), digital versatile disc(DVD)), a smart card, a flash memory device (e.g., card, stick, keydrive), random access memory (RAM), read only memory (ROM), programmableROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM),a register, or a removable disk. Although memory is shown separate fromthe processors in the various aspects presented throughout thisdisclosure, the memory may be internal to the processors (e.g., cache orregister).

Computer-readable media may be embodied in a computer-program product.By way of example, a computer-program product may include acomputer-readable medium in packaging materials. Those skilled in theart will recognize how best to implement the described functionalitypresented throughout this disclosuredepending on the particularapplication and the overall design constraints imposed on the overallsystem.

It is to be understood that the term “signal quality” is non-limiting.Signal quality is intended to cover any type of signal metric such asreceived signal code power (RSCP), reference signal received power(RSRP), reference signal received quality (RSRQ), received signalstrength indicator (RSSI), signal to noise ratio (SNR), signal tointerference plus noise ratio (SINR), etc.

It is to be understood that the specific order or hierarchy of steps inthe methods disclosed is an illustration of exemplary processes. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the methods may be rearranged. The accompanyingmethod claims present elements of the various steps in a sample order,and are not meant to be limited to the specific order or hierarchypresented unless specifically recited therein.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined hereinmay be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. A phrase referring to“at least one of” a list of items refers to any combination of thoseitems, including single members. As an example, “at least one of: a, b,or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, band c. All structural and functional equivalents to the elements of thevarious aspects described throughout this disclosure that are known orlater come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. § 112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

What is claimed is:
 1. A method for wireless communication comprising:starting a reselection timer for reselecting to a neighbor cell when asignal quality of a serving cell is determined to fall below a firstthreshold; and speeding up reselecting to the neighbor cell based atleast in part on a difference between the signal quality of the servingcell and the signal quality of the neighbor cell when the signal qualityof the serving cell falls below a second threshold.
 2. The method ofclaim 1, further comprising speeding up the reselecting to the neighborcell when the difference between the signal quality of the serving celland the signal quality of the neighbor cell is above a third threshold.3. The method of claim 1, in which speeding up the reselecting to theneighbor cell comprises reselecting to the neighbor cell prior to ascheduled expiration of the reselection timer.
 4. The method of claim 1,in which the reselecting occurs prior to a call setup on a userequipment.
 5. The method of claim 1, in which the first threshold is auser equipment (UE) defined threshold.
 6. An apparatus for wirelesscommunication comprising: a memory unit; and at least one processorcoupled to the memory unit, the at least one processor configured: tostart a reselection timer for reselecting to a neighbor cell when asignal quality of a serving cell is determined to fall below a firstthreshold; and to speed up reselecting to the neighbor cell based atleast in part on a difference between the signal quality of the servingcell and the signal quality of the neighbor cell when the signal qualityof the serving cell falls below a second threshold.
 7. The apparatus ofclaim 6, in which the at least one processor is further configured tospeed up the reselecting to the neighbor cell when the differencebetween the signal quality of the serving cell and the signal quality ofthe neighbor cell is above a third threshold.
 8. The apparatus of claim6, in which the at least one processor is further configured to speed upthe reselecting by reselecting to the neighbor cell prior to a scheduledexpiration of the reselection timer.
 9. The apparatus of claim 6, inwhich the reselecting occurs prior to a call setup on a user equipment.10. The apparatus of claim 6, in which the first threshold is a userequipment (UE) defined threshold.
 11. An apparatus for wirelesscommunication comprising: means for starting a reselection timer forreselecting to a neighbor cell when a signal quality of a serving cellis determined to fall below a first threshold; and means for speeding upreselecting to the neighbor cell based at least in part on a differencebetween the signal quality of the serving cell and the signal quality ofthe neighbor cell when the signal quality of the serving cell fallsbelow a second threshold.
 12. The apparatus of claim 11, furthercomprising means for speeding up the reselecting to the neighbor cellwhen the difference between the signal quality of the serving cell andthe signal quality of the neighbor cell is above a third threshold. 13.The apparatus of claim 11, in which the means for speeding up thereselecting to the neighbor cell comprises means for reselecting to theneighbor cell prior to a scheduled expiration of the reselection timer.14. The apparatus of claim 11, in which the reselecting occurs prior toa call setup on a user equipment.
 15. The apparatus of claim 11, inwhich the first threshold is a user equipment (UE) defined threshold.16. A non-transitory computer-readable medium having program coderecorded thereon, the program code executed by a processor andcomprising: program code to start a reselection timer for reselecting toa neighbor cell when a signal quality of a serving cell is determined tofall below a first threshold; and program code to speed up reselectingto the neighbor cell based at least in part on a difference between thesignal quality of the serving cell and the signal quality of theneighbor cell when the signal quality of the serving cell falls below asecond threshold.
 17. The non-transitory computer-readable medium ofclaim 16, in which the program code further comprises program code tospeed up the reselecting to the neighbor cell when the differencebetween the signal quality of the serving cell and the signal quality ofthe neighbor cell is above a third threshold.
 18. The non-transitorycomputer-readable medium of claim 16, in which the program code to speedup the reselecting to the neighbor cell further comprises program codeto reselect to the neighbor cell prior to a scheduled expiration of thereselection timer.
 19. The non-transitory computer-readable medium ofclaim 16, in which the reselecting occurs prior to a call setup on auser equipment.
 20. The non-transitory computer-readable medium of claim16, in which the first threshold is a user equipment (UE) definedthreshold.